Reference is made to commonly assigned U.S. patent application Ser. No. 09/667,293 filed concurrently herewith entitled xe2x80x9cOrganic Electroluminescent Device With Supplemental Cathode Bus Conductorxe2x80x9d by Van Slyke, the disclosure of which is incorporated herein by reference.
The present invention relates generally to organic electroluminescent (EL) devices and more particularly to organic EL devices having contact structures which provide electrical contact between a cathode and a cathode connector of the device.
Passive matrix organic EL devices are fabricated by sandwiching organic EL medium layers between patterned anodes and perpendicularly oriented cathodes. Although full-color passive matrix organic EL devices have been disclosed in U.S. Pat. 5,701,055, a potentially large market exists for monochrome and area-color organic EL devices. In order to meet with demands of this market in a competitive economic environment, methods of device manufacturing have to be found or improved so as to reduce manufacturing costs of such devices.
In a conventional pixelated organic EL device, light-transmissive anodes, for example indium-tin-oxide (ITO) anodes, are formed on a light-transmissive substrate such as, for example, a glass substrate. For relatively small devices, ITO can also be used to form anode and cathode connectors extending inwardly from edges of the substrate for providing electrical connections to driving circuitry to supply driving signals required for operating the organic EL device. For larger area devices, low-resistance metallic connectors are required, at least for the cathodes, to carry electrical currents from an active, pixelated device area to and from the driving circuitry.
Since an organic EL medium layer formed between the anodes and cathodes is relatively electrically insulative, two basic requirements must be met in making a conventional organic EL device: firstly, the organic EL medium layer must be formed, usually by vapor deposition, so that the layer will not cover the portions of the low-resistance metallic connectors which are needed for the electrical connections to the driving circuitry; and secondly, the organic EL medium layer must be formed so that no direct electrical contact between the anodes and the cathodes is possible, i.e. to avoid electrical shorts between the electrodes. In making conventional organic EL devices, these two requirements can be met by selecting a least two separate masking procedures, namely providing a first vapor deposition mask which defines a first deposition zone for forming a defined organic EL medium layer, and providing a second vapor deposition mask which defines a second deposition zone for forming a defined cathode or defined cathodes.
Because organic EL medium layers are sensitive to moisture under ambient conditions, a third requirement of manufacturing organic EL devices is the sequential formation of the organic EL medium layer(s) and the cathode(s) by sequential vapor deposition in a vacuum vapor deposition system without exposing the organic EL medium layer(s) to moisture levels which would prevail under atmospheric conditions outside the vacuum system. While the above first vapor deposition mask can be accurately positioned with respect to the substrate outside the vacuum system, i.e. prior to forming the organic EL medium layer(s), removal of the first mask and accurate positioning of the second mask with respect to the substrate and with respect to the organic EL medium layer(s) by manipulations inside the vacuum system is a relatively complex and time-consuming procedure and may result in misalignment errors.
It is an object of the present invention to provide a method of making an organic EL device by using a single deposition mask defining a deposition zone for vapor depositing an organic EL medium layer and a cathode and by forming a cathode connector shadowing structure for providing electrical contact between a cathode and a cathode connector.
This object is achieved in A method of making a pixelated organic electroluminescent (EL) device, comprising the steps of:
a) providing a light-transmissive substrate having a plurality of spaced light-transmissive anodes formed thereover and at least one cathode connector extending inwardly from an edge of the substrate for providing an electrical connection so that a drive voltage can be applied between a selected anode and at least one cathode to cause light emission from a pixel of the device formed by the selected anode and the at least one cathode;
b) forming an electrically insulative organic cathode connector shadowing structure over the at least one cathode connector;
c) providing a mask defining a deposition zone over the substrate for depositing an electrically insulative organic EL medium layer and a conductive cathode over the organic EL medium layer;
d) first depositing the organic EL medium layer by a vapor deposition of organic EL materials directed towards the substrate into the deposition zone and using a direction of vapor deposition with respect to the cathode connector shadowing structure to cause formation of the organic EL medium layer to terminate at a position spaced from a base of the at least one cathode connector shadowing structure; and
e) second depositing the conductive cathode by a vapor deposition of conductive materials directed towards the organic EL medium layer into the deposition zone and using a direction of vapor deposition with respect to the cathode connector shadowing structure to cause formation of the conductive cathode over the organic EL medium layer, the conductive cathode terminating in electrical contact with the at least one cathode connector in a position where the organic EL medium layer is spaced from the base of the at least one cathode connector shadowing structure.